1. Field of the Invention
The invention relates to an optical sensor sterilizable by irradiation, for determining at least one parameter in a medium, a device comprising such an optical sensor, and a process for producing the sensor and the device. Optical sensors are used particularly in disposable reactors or containers, mixing reactors or containers, and bioreactors or biocontainers in medical technology and biotechnology. In these and similar application areas, it is often necessary to sterilize a container before use. In the field of disposable products, radiation, more particularly gamma radiation, has been found to be effective for sterilization, but is, however, damaging to optical sensors. This is particularly the case for optical sensors based on porous matrices, such as fluorescence-based pH sensors for example. Therefore, such sensors require an effective protective system which, at the same time, can be implemented cost-effectively.
2. Description of the Related Art
WO 02/056023 A1 and DE 10,051,220 A1 disclose optical sensors for measuring at least one parameter in a sample. These sensors are based on a device for exciting the fluorescence of an analyte-sensitive fluorescent dye immobilized in a matrix in a sample vessel or reactor, which dye is in at least indirect contact with the sample, and on an evaluation device for the resulting fluorescence response signal. The analyte concentration can be evaluated or determined in this case by utilizing both the fluorescence decay time and the fluorescence intensity. A disadvantage is that such pH sensor patches, based on a hydrophilic support matrix, such as, for example, impregnated papers or sol-gel matrices, are damaged in a dose-dependent manner during radiation sterilization. There is a reduction in both the intensity of the fluorescence of the dye(s), and the sensitivity of the sensor patch with respect to the measured variable.
U.S. Pat. No. 7,390,462 B2 discloses a sensor in which the fluorescent dye is present immobilized in a hydrophilic matrix. It claims a sensor having the pH-sensitive fluorescent dye MA-HPDS present in a hydrogel. In this case, too, it is a disadvantage that such hydrophilic optical sensors are damaged in a dose-dependent manner during sterilization with gamma radiation. Such radiation is used particularly in laboratory technology for containers composed of polymers. There is a reduction in both the intensity of the fluorescence of the dye(s) and the sensitivity of the sensor with respect to the measured variable. Particularly severe damage to such a sensor patch occurs when it is in contact during the radiation sterilization with a relatively large volume of air, or else with conventional protective gasses such as, for example, nitrogen or argon. During the radiation sterilization, the gasses are partly ionized, or free radicals are generated. These radicals react, for example, during the sterilization of a gas-filled polymer bag, on the wells or else on the sensor surfaces. Sensors based on porous, hydrophilic matrices are particularly vulnerable to this, since the sensor chemistry as a matter of principle has to be present immobilized on the surface, or inner surface, of the matrix, so that the sample to be measured can come into contact with the sensor chemistry. The extent of the damage depends firstly on the irradiation dose and secondly on the ratio of surface area to volume of the irradiated container containing the sensor patch. This ratio determines the number of ions or radicals which damage the sensor patch, or the sensor chemistry contained therein.
DE 10 2009 003 971.6 A1 discloses an optical sensor for measuring at least one parameter, which sensor is porously covered by a noble metal layer, and so reaction of reactive ions on the noble metal layer is achieved. However, a disadvantage in this case is that such a coating is technically and mechanically difficult to achieve and is associated with high costs, and this should be avoided particularly in the field of disposable products.
It is therefore an object of the present invention, firstly, to develop an optical sensor and a device comprising it in which the sensitivity of the optical sensor to radiation, more particularly gamma radiation, is reduced and which is implementable in a cost-effective and simple manner, and, secondly, to specify a process for their production.